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release/21.x: [CodeGenPrepare] Make sure that AddOffset is also a loop invariant (#150625) #150646

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Merged
tru merged 1 commit into from
Jul 29, 2025
Merged

release/21.x: [CodeGenPrepare] Make sure that AddOffset is also a loop invariant (#150625) #150646

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4 changes: 4 additions & 0 deletions llvm/lib/CodeGen/CodeGenPrepare.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2096,6 +2096,10 @@ static bool isRemOfLoopIncrementWithLoopInvariant(
if (!L->isLoopInvariant(RemAmt))
return false;

// Only works if the AddOffset is a loop invaraint
if (AddOffset && !L->isLoopInvariant(AddOffset))
return false;

// Is the PHI a loop increment?
auto LoopIncrInfo = getIVIncrement(PN, LI);
if (!LoopIncrInfo)
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34 changes: 34 additions & 0 deletions llvm/test/Transforms/CodeGenPrepare/X86/fold-loop-of-urem.ll
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Expand Up @@ -1065,3 +1065,37 @@ for.body:
%exitcond.not = icmp eq i32 %inc, %N
br i1 %exitcond.not, label %for.cond.cleanup, label %for.body
}

define i64 @pr150611_add_offset_is_not_loop_invariant(i1 %cond) {
; CHECK-LABEL: define i64 @pr150611_add_offset_is_not_loop_invariant(
; CHECK-SAME: i1 [[COND:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: [[REMAMT:%.*]] = select i1 [[COND]], i64 2, i64 0
; CHECK-NEXT: br label %[[FOR_BODY:.*]]
; CHECK: [[FOR_BODY]]:
; CHECK-NEXT: [[INDVARS:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[INDVARS_NEXT:%.*]], %[[FOR_BODY]] ]
; CHECK-NEXT: [[ADD_OFFSET:%.*]] = zext i1 [[COND]] to i64
; CHECK-NEXT: [[ADD:%.*]] = add nuw i64 [[INDVARS]], [[ADD_OFFSET]]
; CHECK-NEXT: [[REM:%.*]] = urem i64 [[ADD]], [[REMAMT]]
; CHECK-NEXT: [[INDVARS_NEXT]] = add nuw i64 [[INDVARS]], 1
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp eq i64 [[INDVARS_NEXT]], 3
; CHECK-NEXT: br i1 [[EXITCOND]], label %[[FOR_EXIT:.*]], label %[[FOR_BODY]]
; CHECK: [[FOR_EXIT]]:
; CHECK-NEXT: ret i64 [[REM]]
;
entry:
%remamt = select i1 %cond, i64 2, i64 0
br label %for.body

for.body:
%indvars = phi i64 [ 0, %entry ], [ %indvars.next, %for.body ]
%add.offset = zext i1 %cond to i64
%add = add nuw i64 %indvars, %add.offset
%rem = urem i64 %add, %remamt
%indvars.next = add nuw i64 %indvars, 1
%exitcond = icmp eq i64 %indvars.next, 3
br i1 %exitcond, label %for.exit, label %for.body

for.exit:
ret i64 %rem
}
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